Two HIV-positive lymphoma patients who received bone marrow transplants to treat their cancer no longer have detectable virus in their blood cells — even after stopping antiretroviral therapy in recent weeks, researchers reported Wednesday at the International AIDS Society Conference in Kuala Lumpur, Malaysia.

While saying it was too early to declare the men cured, Dr. Timothy Henrich and Dr. Daniel Kuritzkes, both of the division of infectious diseases at Brigham and Women’s Hospital in Boston, called the results “exciting” and said they would help guide scientists’ efforts to fight HIV.

But bone marrow transplants are highly unlikely to become a standard therapy for people with HIV, Henrich said in an interview with The Times.

The news arrives on the heels of several interesting cases where HIV has, apparently, been eradicated in infected patients. In 2007, Timothy Brown, the so-called Berlin Patient, received a bone marrow transplant to treat leukemia; his marrow donor had a mutation that provided resistance to the strain of HIV that Brown had. After a second transplant in 2008, his leukemia was gone. So was his HIV infection. He reportedly remains HIV-free.

In March 2013, doctors reported that a 2-year-old girl in Mississippi had been “functionally cured” of HIV after receiving unusually aggressive antiretroviral treatment shortly after her birth. The girl’s treatments were interrupted when her mother began missing medical appointments — but even after a five-month lapse in treatment, doctors couldn’t detect HIV in her blood.

The two patients in Boston, both men, had been HIV-positive for many years before developing lymphoma, a blood cancer that can be treated, and sometimes even cured, through bone marrow transplants — which essentially give patients new, healthier immune systems.

Like Brown, the men had bone marrow transplants, but of a different sort. The chemotherapy they received before their operations was gentler than that Brown had, leaving more of their original blood cells intact and allowing them to continue their antiretroviral drugs. The transplants they received were of normal cells that did not have the mutation that protects against HIV.

One of the men received his transplant about 4.5 years ago; the other, 2.8 years ago. (A third patient also received a transplant, but died of lymphoma.) At last year’s International AIDS Conference in Washington, Henrich and Kuritzkes reported that after the procedures, neither surviving man had HIV in his blood — but both had continued taking antiretroviral drugs to make sure the virus stayed at bay.

This year, both men dropped the drug regimen, with one patient stopping his medication 15 weeks ago and the other seven weeks ago. When the scientists screened the men’s blood again, collecting billions of cells, they found that the virus was still undetectable — they had achieved at least a 1,000- to 10,000-fold reduction in the virus in the blood.

The team also tested rectal tissue (a major reservoir for the HIV virus) from one of the patients. There, too, the virus was undetectable.

Henrich, who noted that the virus could still be lurking in the patients’ bodies — in brain tissue, for instance — said he was “of the camp where I don’t know if I will ever be able to say patients are cured,” but that if the men remained HIV-free for a year or two, “the chances of the virus coming back will be very small.”

That said, he added, it doesn't make sense to perform bone marrow transplants to treat HIV-positive people who don’t have cancer. There are many risks associated with the expensive procedure, with 15% to 20% of patients dying from complications from the treatment itself rather than their cancer, Henrich said.

“Unfortunately, it’s not going to be a practical strategy,” he said.

But he also said the data the team had gathered would help guide new strategies for eradicating the virus.

“It will help us figure out what’s going on in terms of viral persistence,” Henrich said. “How low do we need to get the viral counts? How can we use the immune system to fight it?”